Multi-2DEG HEMT

Abstract

A high electron mobility field effect semiconductor device includes a layer stack including electron supply layers and electron transport layers to form a plurality of hetero-junctions so as to provide 2DEG layers in hetero-interfaces on the electron transport layer side, a source electrode and a drain electrode disposed with an interval on a surface of the layer stack to oppose each other and to be conductive to the 2DEG layers, and a gate electrode extending between the source and drain electrodes to develop a Schottky contact with the upper-most carrier supply layer. The electron supply layer remote from the gate electrode has an electron density higher than that of the electron supply layer less remote from the gate electrode.

We claim: 
     
       1. A high electron mobility field effect semiconductor device comprising: a layer stack including carrier supply layers and carrier transport layers forming a plurality of hetero-junctions so as to provide two-dimensional carrier gas layers in hetero-interfaces on the carrier transport layer side;   a source electrode and a drain electrode, the electrodes being disposed with an interval on a surface of the layer stack to oppose each other and to be conductive to form electrical connection with the two-dimensional carrier gas layers; and   a gate electrode extending between the source and drain electrodes to form a Schottky contact with an upper-most one of said carrier supply layers, wherein one of said carrier supply layers remote from the gate electrode has a carrier density higher than that of another of said carrier supply layers less remote from the gate electrode.     
     
     
       2. A high electron mobility field effect semiconductor device according to claim 1, wherein: one of said carrier supply layers less remote from the gate electrode is uniformly doped; and another of said carrier supply layers remote from the gate electrode is planar-doped.   
     
     
       3. A high electron mobility field effect semiconductor device comprising: a layer stack including carrier supply layers and carrier transport layers forming a plurality of hetero-junctions so as to provide two-dimensional carrier gas layers in hetero-interfaces on the carrier transport layer side;   a source electrode and a drain electrode, the electrodes being disposed with an interval on a surface of the layer stack to oppose each other and to be conductive to form electrical connection with the two-dimensional carrier gas layers; and   a gate electrode extending between the source and drain electrodes to form a Schottky contact with an upper-most one of said carrier supply layers, wherein one of said carrier transport layers remote from the gate electrode is formed of such material that an effective mass of carriers therein is smaller than that of carrier in another of said carrier transport layers less remote from the gate electrode,   said carrier transport layers comprise three or more layers including InGaAs layers on a remote side from the gate electrode, one of said InGaAs layers remote from the gate electrode has a higher In composition than that of another of said InGaAs layers less remote from the gate electrode.     
     
     
       4. A high electron mobility field effect semiconductor device having a hetero-structure, the semiconductor device comprising: a layer stack including carrier supply layers and carrier transport layers forming a plurality of hetero-junctions so as to provide two-dimensional carrier gas layers in hetero-interfaces on the carrier transport layer side;   a source electrode and a drain electrode, the electrodes being disposed with an interval on a surface of the layer stack to oppose each other to be conductive to form electrical connection with the two-dimensional carrier gas layers; and   a gate electrode extending between the source and drain electrodes to form a Schottky contact with an upper-most one of said carrier supply layers, wherein one of said carrier transport layers remote from the gate electrode is formed of such material that an effective mass of carriers therein is smaller than that of carriers in another of said carrier transport layers less remote from the gate electrode,   said carrier transport layers comprise three or more layers including InGaAs layers on a remote side from the gate electrode, one of said InGaAs layers remote from the gate electrode has a higher In composition than that of another of said InGaAs layers less remote from the gate electrode, wherein: the hetero-structure includes at least three hetero-junctions; and   each of said carrier transport layers remote from the gate electrode comprises InGaAs,   composition of In in said InGaAs carrier transport layers is set to a larger value as a distance between the gate electrode and the carrier transport layer is increased.       
     
     
       5. A high electron mobility field effect semiconductor device comprising: a layer stack including carrier supply layers and carrier transport layers, forming a plurality of hetero-junctions so as to provide a two-dimensional carrier gas layers in hetero-interfaces on the carrier transport layer side;   a source electrode and a drain electrode, the electrodes being disposed with an interval on a surface of the layer stack to oppose each other and to be conductive to form electrical connection with the two-dimensional carrier gas layers; and   a gate electrode extending between the source and drain electrodes to form a Schottky contact with an upper-most one of said carrier supply layers, wherein: one of said carrier supply layers less remote from the gate electrode is uniformly doped; and   another of said carrier supply layers remote from the gate electrode is planar-doped, wherein: there are formed at least three hetero-junctions; and   a carrier density of the planar doped carrier supply layer is set so that the carrier density of the planar doped carrier supply layer becomes higher as the distance between the gate electrode and the planar doped carrier supply layer is increased.